Epidermal growth factor (EGF) is a polypeptide capable of stimulating proliferation of a wide range of cell types in vitro. In one of the present studies, EGF extracted from the submaxillary gland of mice was found to exist in multiple forms which can be isolated by high-performance liquid chromatography. Compositional differences, so far, cannot be demonstrated between Alpha- and Beta-EGF, the two major forms. Neither of the purified forms convert to the other after isolation or exposure to urea. Administration of 125I-Alpha-EGF intravenously to pregnant mice revealed rapid clearance and degradation of the labeled peptide but no evidence for placental transfer of the intact peptide. Gel chromatography of extracts of embryos from 13 day pregnant CD-1 mice revealed that most of the material inhibiting 125I-EGF binding to liver membranes was associated with peptides that did not co-elute with EGF. In another study, EGF is being examined as a putative mediator of estrogen-induced uterine epithelial cell proliferation. Uterine tissue will be studied for binding of 125I-EGF to membrane preparations, autoradiographic localization of receptors, immunolocalization of EGF, and histologic changes following direct introduction of EGF into the uterine cavity.